The present invention relates to torque generator steering devices, and more particularly, to such devices in which a relatively low torque steering input is translated into a relatively high torque steering output, with the assistance of a source of pressurized fluid.
Torque generators of the type to which the present invention relates have been in commercial use for many years, have been commercially quite successful, and are illustrated and described in greater detail in U.S. Pat. Nos. Re. 25,291 and 4,936,094, both of which are assigned to the assignee of the present invention and are incorporated herein by reference.
In the typical prior art torque generator of the type illustrated and described in the above-incorporated patents, there are three sections: (1) an input section including an input shaft; (2) a fluid displacement mechanism (typically a gerotor gear set); and (3) a valving section, including an output shaft. In the commercially available torque generators, these three sections have always been arranged "serially", i.e., one section after another, axially, starting with the input section and ending with the output section. As a result, the commercial torque generators have been fairly large (i.e., long in the axial direction).
Although the prior art torque generator has been commercially successful, and its design has remained basically unchanged for many years, its market penetration has been somewhat hindered by the overall size of the device. For example, there are many small tractors in use on which torque generator steering devices could be applied on an "after-market" basis, but the overall length of the prior art torque generator prevents it from physically fitting within the available length of the steering column on a number of tractors.
The torque generator currently commercially available from the assignee of the present invention includes two sets of internal splines, and two dogbone shafts which together include three sets of crowned, external splines. The result can be an undesirable amount of looseness or backlash in the mechanical connection between the input shaft and the output shaft, thus hindering the use of the prior art torque generator in certain vehicle applications.